Wednesday's fireball over the US southwest was not UARS
It was definitely not UARS though. Not only was UARS still being tracked and hence in orbit after the fireball appeared (approx. 19:45 MST on the 14th, or 2:45 UTC on the 15th): but it was simply not passing over that part of the USA at that time. It was hence not UARS, or a piece of UARS.